Magnetic materials



Pa tented June 2 2 1948 MAGNETIC MA-EERIAES' EthanA. Nesbitt, Chatham, N. J. assignor to. Bell.v

Telephone. Laboratories, Incorporated, New York, N. Y., a corporationofi New York No Drawing. Application July; 1.0;, was;

SelifikNO. 60.45294 This invention relates to. permanent. magnet alloys, andv to magnets produced. therefrom. which are caused to have more desirable properties asv permanent magnets by a cold working treatment. The invention also" relates to and includes methods of treating and: producing; such improved a1- loys and permanent magnets.

An object of the invention is the production of better and more efficient permanent magnet materials.

This present application is a continuation-in part of my copending application, Serial No. 416,216, filedOctober 23. 1.94 whichis now. Patent 'No. 2,382,649, d'ated'August 14, 1945, and" which in. turn was. a continuation-impart of a former application copending therewith, namely. Serial No. 3ll,' 735', filed; December 30, I939; which is now Patent. No. 2,298,225; dated: October 6, 1942; for which reason the priority benefits of the filing dates; of said applications are claimed for the present application to whatever extent and under whatever conditions of law-may be ap-- plicable.

A feature of the present invention isthedis'--- covery that permanent magnet compositions, such as those described hereinafter. may be improved by reduction of the cross section thereof by a stage of coldworking during their preparation and prior to the final heat treatment. Such working is preferably accomplished by methods which produce elongation and prevent lateral spreading. Methods that have been -found benefici-al include swaging, rolling with. grooved rolls. andwire drawing. It. appears. that; the resultof improved permanent magnet properties: is. manitested chiefly in. the direction of. elongation. Reduction of thickness by such rollingof a metal. sheet, as permits the-material to. spread laterally is only partially effective.

The evidence. is that materials or orproduced accordi-ng to. the present. invention generally. are:

anisotropic. and. theirv improved properties are manifested chiefly in. the direction in which theelongationtakes place.

In the said. application, SerialNo, 31137.35. it; is; pointed out that; there are classes of materialswhich, if maintained at a certain high tempera-- tune but below. the; melting, point-, assume aform known as the gamma phase? and if thematerial is thereafter cooled to around roomtemperature, it tends to assume the alphaf phase: and thereafter. it maintained at. around. 5.00.? to 800, a finely dispersed small amount. of. the. gamma phase forms in. the: "alpha phase. This brief statement istcbe read inthe light-ofithe. informs..-

' tion, diagrams. and discussion of said. applicationLSerial No. 311.735..

As pointed out. in. the said application, now Patent No. 2,298,225,. dated October 6', 1942, a. suitable procedure for preparing permanent mag;- net material is. to elt the material and cool to room temperature. to produce formation of the, alpha phase, and. thereafter elevate the material to a higher temperature between 50.05" ('1. to 8.0.0. C. for. a. lengthy of time such. as is necessary to. allow a small amount, of the gamma? phase. to. precipitate in a highly dispersed form in the alpha. phase, Thi'sproduces dispersion hardening in, the material and produces a very; effective. permanent magnet material. This method of. forming permanent magnet materials different and seemingly involves a different principle from that heretofore employed with respect to many others, such as alloys of iron, cobalt and molybdenum in that, in the present instance. the. material is converted; into a lowtemperature. alpha phase andthereafter-has a, small amount of the high temperature gamma phase precipitated therein in a fine and; dispersed state. In the usual case of permanent magnetshardenedby precipitation the high temperature phase is preserved and a small amount of the low temperature phase is precipitated;

In some alloys of the type under discussion the gamma to alphatransformation tends tooccur at, low temperatures at,which the transformation becomes sluggish andnon-equilibriumconditions exist.

Whether this is the case or not, cold rolling these. alloys. in groovedi rolls or working them mechanically by any. equivalent method causes. or expedites the formation at room, temperature of. the alpha phase. and. brings them into, equilibrium. Some-alloys of this, type may not change. completely tothe alpha phase at. room temperature,- unless given they above treatment. Others. change. to, alpha phase only, in part. This. resultlwhether whole. or partialis one beneficial aspect ofthepresent invention. Howeven there. is a. second beneficial aspect. which, is due to, crystal orientation. X-ray. measurements confirm this and magnetic tests show the best. per-- manent. magnet. properties in. the direction. of elongation Either. or: both. of these beneficial aspects. may be present in, varying degrees.

After the alloys. are brought completely or mainly into the alpha phase by the combination or cooling and' cold working they are raised to a temperature in. the. range of temperatures which causes; the. precipitation in finelydispersed par.-

ticles of some of the gamma phase. This results in the production of magnetic material having efiective and desirable properties as permanent magnets in the direction of elongation. In every case care must be used not to raise the material to too high a temperature in order not to lose the efiect of cold working. I

A frequently used criterion of the desirability of permanent magnet materials is the product of coercive force and residual induction. A more accurate figure of merit is that of maximum energy product, which on the demagnetization portion of the hysteresis loop, is the product of induction B and magnetizing force H at a point Where this product is the greatest. See Wall, Applied Magnetism, pages 42 to 45 inclusive.

The above criterion is independent of the matter of cost, ease or difiiculty of preparation, rolling or drawing, brittleness, availability of raw materials and other factors which must receive consideration for many practical purposes and applications. Thus a permanent magnet com position which has an absolute maximum energy product? less than some other which is less available or suitable for some one or more of the above aspects may be a valuable contribution to the art if, for example, it may be made to possess a considerably greater maximum energy produc Among objects of the present invention are to provide better permanent magnets at little or no increase in cost; to produce useful perma nent magnets from materials not hitherto known to possess permanent magnet properties to a useful extent; to improve the properties of compositions known to have useful permanent magnet properties; to produce useful permanent magnets from cheap or readily available raw materials; to increase either or both the product of coercive force and residual induction or the maximum energy produc of magnetic materials; to provide elongated magnetic materials such as tapes and strips having useful maximum energy products; and to provide useful magnets from materials which may ,be worked with facility.

The subjectmatter of the invention or discovery comprises a range or group of magnetic alloys which by appropriate combined heat treatment and cold rolling or elongating treatment will have one or the other or both of the abovenamed magnetic products or the coercive force or the residual induction increased in the direction of elongation by from one hundred to several hundred per cent as compared to the material in the cast or unsuitably heat treated or unsuitably worked condition.

A feature of the invention or discovery is the lack of any necessity for quenching the material at any time in order to improve its properties; however, rapid cooling after casting may be practiced. One of the beneficial aspects of the discovery is that the cooling rates may vary widely as convenience or necessity demands.

The alloys may be prepared in the form of rods, bars, wire or tapes. A suitable treatment for any specimen is first to give it the desired amount of cold working plus a low temperature bake. No other heat treatment is necessary. Satisfactory results have been obtained with reductions in area of '75 per cent, although this exact amount is by no means critical.

In greater detail, the material is cast, which gives it the necessary high temperature treatment; it may be given a further or special heat 4 treatment at around 800 to 1300 C. The cooled material, which may be cooled to room temperature slowly or rapidly, and must be cooled sub- I stantially below about 600 C. is forcibly elon gated by rolling with grooved rolls, swaging, drawing through dies or by combinations of these methods or by any similar method or methods so as to reduce the cross section in one or several steps over a range from a small amount to a small fraction of the original cross section. The material is then heated to a temperature gen orally in the region 590 to 800 C. and maintained for a sufficient time such as a matter of seconds or minutes at the higher temperature to one to'several hours at the lower temperature, but somewhat more as the temperature ap-v proaches the bottom of the range. Too high a temperature destroys the effect of the cold rolling, and too low a temperature or too short a time is only partially effective. A quenching treatment is unnecessary.

Compositions which respond to this type of treatment are:

Per cent Per cent Per cent Per cent Iron Cobalt Manganese Vanadium Carbon above about 0.1 per cent is not an essential constituent and in fact is absent from these materials.

The constituents may in general vary over a range which includes iron from 49 per cent to '72 per cent, cobalt from 4 per cent to 21 per cent, manganese from 18 per cent to 22 per cent, and vanadium from 4 per cent to 12 per cent; these elements are the essential constituents of compositions according to the invention except [for minor impurities generally totalling not over 1 per cent, except, as stated above, the carbon content isquite low.

Thus there are described certain permanent magnet materials, an improvement in them by a heat treatment, a further and often considerable improvement by a cold Working treatment, and avoidance of necessity for quenching. These compositions possess or may be made to possess substantial permanent magnet properties and are notably improved in properties by a treatment of the .kind described. They may be prepared from raw materials which are ordinarily cheap and readily available. They respond to the described treatment and may be made to acquire magnetic properties increased as a result of the treatment described ascompared with identical compositions as cast. In some cases the increase in energy product due to cold rolling may be per cent as compared to the same material heat treated but not cold rolled.

The apparatus illustrated in the above-noted Patent 2,298,225, or any other suitable apparatus, may be used to perform the cold rolling or elongating process.

The finished magnets may be magnetized by per cent vanadium, these constituents comprising the entire constituents of the composition except for minor impurities not over 1 per cent.

2. An article having properties adapted for permanent magnet use composed of an alloy comprising as essential constituents 49 per cent to 72 per cent iron, 4 per cent to 21 per cent cobalt, 18 per cent to 22 per cent manganese, and 4 per cent to 12 per cent vanadium, these constituents comprising the entire constituents of the composition except for minor impurities not over 1 per cent, said article produced by causing the alloy to pass into the temperature range of from 800 C. to 1300 C., cooling it substantially below 600 C., forcibly elongating the material in the cold condition and thereafter maintaining it in the range 500 C. to 800 C. without exceeding about 800 C. whereby the material is caused to have increased ability to retain permanent magnetism in the direction of elongation.

3. A permanent magnet having the following constituents within about 1 per cent variation for each constituent: 71 per cent iron, 5 per cent cobalt, 20 per cent manganese, and the balance consisting of vanadium and incidental impurities.

4. A permanent magnet having the following constituents within about 1 per cent variation for each constituent: per cent iron, 20 per cent cobalt, 20 per cent manganese, and the balance consisting of vanadium and incidental impurities.

5. A permanent magnet having the following constituents within about 1 per cent variation for each constituent: per cent iron, 10 per cent cobalt, 20 per cent manganese, and the balance consisting of vanadium and incidental impurities.

ETHAN A. NESBITT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Nesbitt Aug. 14, 1945 Number 

